Traditionally, displays present information in two dimensions. Images displayed by such displays are planar images that lack depth information. Because people observe the world in three-dimensions, there have been efforts to provide displays that can display objects in three-dimensions. For example, stereo displays convey depth information by displaying offset images that are displayed separately to the left and right eye. When an observer views these planar images they are combined in the brain to give a perception of depth. However, such systems are complex and require increased resolution and processor computation power to provide a realistic perception of the displayed objects.
Multi-component displays including multiple display screens in a stacked arrangement have been developed to display real depth. Each display screen may display its own image to provide visual depth due to the physical displacement of the display screens. For example, multi-display systems are disclosed in U.S. Patent Publication Nos. 2015/0323805 and 2016/0012630, the disclosures of which are both hereby incorporated herein by reference.
When first and second displays or display layers are conventionally stacked on each other in a multi-display system, moire interference occurs. The moire interference is caused by interactions between the color filters within the layers when projected onto a viewer's retina. For example, when green color filters overlap, light is transmitted making for a comparative bright patch. When a green filter is over say a red filter, not as much light will be transmitted making for a dark region. Since the rear and front displays or display layers have slightly different sizes when projected onto the retina, the pixels will slowly change from being in phase to out of phase. This has the effect of producing dark and bright bands otherwise known as moire interference.
There have been several approaches attempting to remove moire interference in a multi-layer display (MLD) system. Certain MLD systems solely utilize diffusive optics to blur the rear-most display layer. This approach suffers from the following limitations: (a) the rear most image is inherently blurry—there is a trade-off between reducing moire interference and the clarity of the rear most image display layer; (b) the diffusing element utilizes a specialized diffuser pattern, which is difficult to obtain; and (c) the diffusing element sits between polarizers and both the film substrate and stiffener substrate must be free of any birefringence. As a result, MLD systems using solely a diffuser to address moire issues do not provide an ideal solution to reducing moire interference, especially when those systems have reduced form factors. Historic and present methodologies that rely only on diffusers to address moire interference do not provide an acceptable solution to the moiré issue without the introduction of significant and detrimental side-effects to image quality.
Certain example embodiments of the instant invention provide solution(s) that make moiré interference in MLD systems vanish or substantially vanish, but without significantly sacrificing the rear display resolution and contrast. In certain example embodiments of this invention, the MLD system includes first and second displays. Sub-pixel compression is utilized in order to reduce or eliminate moire interference. For example, when the rear display of a MLD system has red (R), green (G), and blue (B) color filter aligned in respective columns (or rows), physical sub-pixel compression remaps the R, G and B sub-pixels based on their color into a single combined stripe (in the column or row direction) which may be white (W). It is possible to use the method of sub-pixel compression to construct a multilayer optical element that turns or compresses the red and blue sub-pixels onto the green sub-pixel (e.g., via a diffraction based grating, prism(s), and/or splitting device(s)), thereby forming a white line. This changes the rear display's RGB color filter pattern of a given subpixel or pixel area into a single white stripe or area, which removes color filter interaction between display layers and can reduce moire interference. The white stripe or area may then be copied to the left and/or right in order to expand it out again (e.g., via a kernel such as a refractive beam mapper (RBM) which may be square shaped for instance) as it proceeds toward the front display of the MLD system.
In certain example embodiments of this invention, there is provided a display device comprising: a first display in a first plane for displaying a first image; a second display in a second plane for displaying a second image, wherein said first and second planes are approximately parallel to each other; a subpixel compressing structure provided between the first and second displays for reducing moire interference, the subpixel compressing structure comprising a first optical element for compressing red light from a red subpixel, green light from a green subpixel, and blue light from a blue subpixel into a white area, and a second optical element for spreading the white area.
Sub-pixel compression may or may not be used in combination with other techniques for reducing moire interference (e.g., color filter offset or dissimilar color filter patterns on the respective displays, diffuser techniques, and/or refractive element techniques) in various embodiments of this invention.